Federal Register / Vol. 86, No. 138 / Thursday, July 22, 2021 / Proposed Rules 38643 

2011), the EPA has offered consultation 

to tribal governments that may be 

affected by this action. 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

EPA interprets Executive Order 13045 

as applying only to those regulatory 

actions that concern environmental 

health or safety risks that the EPA has 

reason to believe may 

disproportionately affect children, per 

the definition of ‘‘covered regulatory 

action’’ in section 2–202 of the 

Executive Order. This action is not 

subject to Executive Order 13045 

because it merely proposes to 

disapprove a SIP submission as not 

meeting the CAA. 

H. Executive Order 13211, Actions That 

Significantly Affect Energy Supply, 

Distribution or Use 

This action is not subject to Executive 

Order 13211, because it is not a 

significant regulatory action under 

Executive Order 12866. 

I. National Technology Transfer and 

Advancement Act 

This rulemaking does not involve 

technical standards. 

J. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-Income Populations 

EPA believes the human health or 

environmental risk addressed by this 

action will not have potential 

disproportionately high and adverse 

human health or environmental effects 

on minority, low-income or indigenous 

populations. This action merely 

proposes to disapprove a SIP 

submission as not meeting the CAA. 

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Intergovernmental relations, 

Nitrogen dioxide, Ozone, Particulate 

matter, Sulfur oxides, Visibility 

transport. 

Authority: 42 U.S.C. 7401 et seq. 

Dated: July 15, 2021. 

David Gray, 

Acting Regional Administrator, Region 6. 

[FR Doc. 2021–15467 Filed 7–21–21; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

[EPA–R05–OAR–2021–0256; FRL–8692–01– 

R5] 

Air Plan Approval; Wisconsin; 

Attainment Plan for the Rhinelander 

SO2 Nonattainment Area 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: The Environmental Protection 

Agency (EPA) is proposing to approve 

the State Implementation Plan (SIP) 

revision submitted by Wisconsin on 

March 29, 2021, which amends a SIP 

submission previously submitted to 

EPA on January 22, 2016 and 

supplemented on July 18, 2016, and 

November 29, 2016, for attaining the 1- 

hour sulfur dioxide (SO2) primary 

national ambient air quality standard 

(NAAQS) for the Rhinelander SO2

nonattainment area. This plan (herein 

referred to as Wisconsin’s Rhinelander 

SO2 plan or plan) includes Wisconsin’s 

attainment demonstration and other 

elements required under the Clean Air 

Act (CAA). In addition to an attainment 

demonstration, the plan addresses the 

requirement for meeting reasonable 

further progress (RFP) toward 

attainment of the NAAQS, reasonably 

available control measures and 

reasonably available control technology 

(RACM/RACT), and contingency 

measures. This action supplements a 

prior action which found that 

Wisconsin had satisfied emission 

inventory and new source review (NSR) 

requirements for this area, but had not 

met requirements for the elements 

proposed to be approved here. EPA is 

proposing to conclude that Wisconsin 

has appropriately demonstrated that the 

plan provisions provide for attainment 

of the 2010 1-hour primary SO2 NAAQS 

in the Rhinelander SO2 nonattainment 

area and that the plan meets the other 

applicable requirements under the CAA. 

DATES: Comments must be received on 

or before August 23, 2021. 

ADDRESSES: Submit your comments, 

identified by Docket ID No. EPA–R05– 

OAR–2021–0256 at http://

www.regulations.gov, or via email to 

leslie.michael@epa.gov. For comments 

submitted at Regulations.gov, follow the 

online instructions for submitting 

comments. Once submitted, comments 

cannot be edited or removed from 

Regulations.gov. For either manner of 

submission, EPA may publish any 

comment received to its public docket. 

Do not submit electronically any 

information you consider to be 

Confidential Business Information (CBI) 

or other information whose disclosure is 

restricted by statute. Multimedia 

submissions (audio, video, etc.) must be 

accompanied by a written comment. 

The written comment is considered the 

official comment and should include 

discussion of all points you wish to 

make. EPA will generally not consider 

comments or comment contents located 

outside of the primary submission (i.e., 

on the web, cloud, or other file sharing 

system). For additional submission 

methods, please contact the person 

identified in the FOR FURTHER

INFORMATION CONTACT section. For the 

full EPA public comment policy, 

information about CBI or multimedia 

submissions, and general guidance on 

making effective comments, please visit 

http://www2.epa.gov/dockets/ 

commenting-epa-dockets. 

FOR FURTHER INFORMATION CONTACT: 

Abigail Teener, Environmental 

Engineer, Attainment Planning and 

Maintenance Section, Air Programs 

Branch (AR–18J), Environmental 

Protection Agency, Region 5, 77 West 

Jackson Boulevard, Chicago, Illinois 

60604, (312) 353–7314, teener.abigail@

epa.gov. The EPA Region 5 office is 

open from 8:30 a.m. to 4:30 p.m., 

Monday through Friday, excluding 

Federal holidays and facility closures 

due to COVID–19. 

SUPPLEMENTARY INFORMATION: This 

SUPPLEMENTARY INFORMATION section is 

arranged as follows: 

I. Why was Wisconsin required to submit an 

SO2 plan for the Rhinelander area? 

II. Requirements for SO2 Nonattainment Area 

Plans 

III. Attainment Demonstration and Longer 

Term Averaging 

IV. Review of Modeled Attainment Plan 

A. Model Selection 

B. Simulation of Downwash 

C. Meteorological Data 

D. Emissions Data 

E. Emission Limits 

F. Background Concentrations 

G. Summary of Results 

V. Review of Other Plan Requirements 

A. RACM/RACT 

B. Reasonable Further Progress (RFP) 

C. Contingency Measures 

VI. What action is EPA taking? 

VII. Incorporation by Reference 

VIII. Statutory and Executive Order Reviews 

I. Why was Wisconsin required to 

submit an SO2 plan for the Rhinelander 

area? 

On June 22, 2010, EPA promulgated a 

new 1-hour primary SO2 NAAQS of 75 

parts per billion (ppb), which is met at 

an ambient air quality monitoring site 

when the 3-year average of the annual 

99th percentile of daily maximum 1- 


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1 86 FR 15418 (March 23, 2021). 

2 79 FR 60064 (October 6, 2014). 

hour average concentrations does not 

exceed 75 ppb, as determined in 

accordance with appendix T of 40 CFR 

part 50. See 75 FR 35520, codified at 40 

CFR 50.17(a)–(b). On August 5, 2013, 

EPA designated 29 areas of the country 

as nonattainment for the 2010 SO2

NAAQS, including the Rhinelander area 

within the State of Wisconsin. See 78 

FR 47191, codified at 40 CFR part 81, 

subpart C. These area designations were 

effective October 4, 2013. Section 191 of 

the CAA directs states to submit SIPs for 

areas designated as nonattainment for 

the SO2 NAAQS to EPA within 18 

months of the effective date of the 

designation, i.e., by no later than April 

4, 2015 in this case. These SIPs are 

required to demonstrate that their 

respective areas will attain the NAAQS 

as expeditiously as practicable, but no 

later than 5 years from the effective date 

of designation, which is October 4, 

2018. 

In response to the requirement for SO2

nonattainment plan submittals, 

Wisconsin submitted a nonattainment 

plan for the Rhinelander area on January 

22, 2016, and supplemented it on July 

18, 2016, and November 29, 2016. On 

March 23, 2021,1 EPA partially 

approved and partially disapproved 

Wisconsin’s Rhinelander SO2 plan as 

submitted and supplemented in 2016. 

EPA approved the base-year emissions 

inventory and affirmed that the new 

source review requirements for the area 

had previously been met.2 EPA also 

approved the SO2 emission limit for 

Ahlstrom-Munksjo ̈’s Rhinelander 

facility (Ahlstrom-Munksjo ̈) (formerly 

Expera Specialty Solutions LLC 

(Expera)) as SIP-strengthening. At that 

time, EPA disapproved the attainment 

demonstration, since the plan relied on 

credit for more stack height than is 

creditable under the regulations for 

good engineering practice (GEP) stack 

height. Additionally, EPA disapproved 

the plan for failing to meet the 

requirements for meeting RFP toward 

attainment of the NAAQS, RACM/ 

RACT, emission limitations and control 

measures as necessary to attain the 

NAAQS, and contingency measures. 

Under sections 110(c) and 179(a)–(b) 

of the CAA, a disapproval in whole or 

in part of a state submittal initiates a 

Federal Implementation Plan (FIP) clock 

and sanctions clocks, respectively, 

which are terminated by an EPA 

rulemaking approving a revised plan. 

On March 29, 2021, Wisconsin 

submitted a permit containing a revised 

emission limit and supplemental 

information in order to remedy the 

plan’s deficiencies specified in EPA’s 

March 23, 2021 rulemaking, along with 

a request that EPA approve its revised 

plan for the Rhinelander area. 

The remainder of this action describes 

the requirements that SO2

nonattainment plans must meet in order 

to obtain EPA approval, provides a 

review of Wisconsin’s revised plan with 

respect to these requirements, and 

describes EPA’s proposed action on the 

plan. 

II. Requirements for SO2

Nonattainment Area Plans 

Nonattainment SIPs must meet the 

applicable requirements of the CAA, 

and specifically CAA sections 172, 191 

and 192. EPA’s regulations governing 

nonattainment SIPs are set forth at 40 

CFR part 51, with specific procedural 

requirements and control strategy 

requirements residing at subparts F and 

G, respectively. Soon after Congress 

enacted the 1990 Amendments to the 

CAA, EPA issued comprehensive 

guidance on SIPs, in a document 

entitled the ‘‘General Preamble for the 

Implementation of Title I of the Clean 

Air Act Amendments of 1990,’’ 

published at 57 FR 13498 (April 16, 

1992) (General Preamble). Among other 

things, the General Preamble addressed 

SO2 SIPs and fundamental principles for 

SIP control strategies. Id., at 13545–49, 

13567–68. On April 23, 2014, EPA 

issued recommended guidance for 

meeting the statutory requirements in 

SO2 SIPs, in a document entitled, 

‘‘Guidance for 1-Hour SO2

Nonattainment Area SIP Submissions,’’ 

available at https://www.epa.gov/sites/ 

production/files/2016-06/documents/ 

20140423guidance_nonattainment_

sip.pdf. In this guidance EPA described 

the statutory requirements for a 

complete nonattainment area SIP, which 

includes: An accurate emissions 

inventory of current emissions for all 

sources of SO2 within the 

nonattainment area; an attainment 

demonstration; demonstration of RFP; 

implementation of RACM (including 

RACT); NSR; emissions limitations and 

control measures as necessary to attain 

the NAAQS; and adequate contingency 

measures for the affected area. EPA 

already concluded in its March 23, 2021 

rulemaking that Wisconsin has met the 

emissions inventory and NSR 

requirements. 

In order for EPA to fully approve a 

SIP as meeting the requirements of CAA 

sections 110, 172 and 191–192 and 

EPA’s regulations at 40 CFR part 51, the 

SIP for the affected area needs to 

demonstrate to EPA’s satisfaction that 

each of the aforementioned 

requirements have been met. Under 

CAA sections 110(l) and 193, EPA may 

not approve a SIP that would interfere 

with any applicable requirement 

concerning NAAQS attainment and 

RFP, or any other applicable 

requirement, and no requirement in 

effect (or required to be adopted by an 

order, settlement, agreement, or plan in 

effect before November 15, 1990) in any 

area which is a nonattainment area for 

any air pollutant, may be modified in 

any manner unless it ensures equivalent 

or greater emission reductions of such 

air pollutant. 

III. Attainment Demonstration and 

Longer Term Averaging 

CAA section 172(c)(1) directs states 

with areas designated as nonattainment 

to demonstrate that the submitted plan 

provides for attainment of the NAAQS. 

40 CFR part 51, subpart G, further 

delineates the control strategy 

requirements that SIPs must meet, and 

EPA has long required that all SIPs and 

control strategies reflect four 

fundamental principles of 

quantification, enforceability, 

replicability, and accountability. 

General Preamble at 13567–68. SO2

attainment plans must consist of two 

components: (1) Emission limits and 

other control measures that ensure 

implementation of permanent, 

enforceable and necessary emission 

controls, and (2) a modeling analysis 

which meets the requirements of 40 CFR 

part 51, appendix W, which 

demonstrates that these emission limits 

and control measures provide for timely 

attainment of the primary SO2 NAAQS 

as expeditiously as practicable, but by 

no later than the attainment date for the 

affected area. In all cases, the emission 

limits and control measures must be 

accompanied by appropriate methods 

and conditions to determine compliance 

with the respective emission limits and 

control measures and must be 

quantifiable (i.e., a specific amount of 

emission reduction can be ascribed to 

the measures), fully enforceable 

(specifying clear, unambiguous and 

measurable requirements for which 

compliance can be practicably 

determined), replicable (the procedures 

for determining compliance are 

sufficiently specific and non-subjective 

so that two independent entities 

applying the procedures would obtain 

the same result), and accountable 

(source specific limits must be 

permanent and must reflect the 

assumptions used in the SIP 

demonstrations). 

EPA’s April 2014 guidance 

recommends that the emission limits be 

expressed as short-term average limits 

(e.g., addressing emissions averaged 


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3An ‘‘average year’’ is used to mean a year with 

average air quality. While 40 CFR 50 appendix T 

provides for averaging three years of 99th percentile 

daily maximum values (e.g., the fourth highest 

maximum daily concentration in a year with 365 

days with valid data), this discussion and an 

example below uses a single ‘‘average year’’ in order 

to simplify the illustration of relevant principles. 

over one or three hours), but also 

describes the option to utilize emission 

limits with longer averaging times of up 

to 30 days so long as the state meets 

various suggested criteria. See 2014 

guidance, pp. 22 to 39. The guidance 

recommends that, should states and 

sources utilize longer averaging times, 

the longer term average limit should be 

set at an adjusted level that reflects a 

stringency comparable to the 1-hour 

average limit at the critical emission 

value shown to provide for attainment 

that the plan otherwise would have set. 

The April 2014 guidance provides an 

extensive discussion of EPA’s rationale 

for concluding that appropriately set 

comparably stringent limitations based 

on averaging times as long as 30 days 

can be found to provide for attainment 

of the 2010 SO2 NAAQS. In evaluating 

this option, EPA considered the nature 

of the standard, conducted detailed 

analyses of the impact of use of 30-day 

average limits on the prospects for 

attaining the standard, and carefully 

reviewed how best to achieve an 

appropriate balance among the various 

factors that warrant consideration in 

judging whether a state’s plan provides 

for attainment. Id. at pp. 22 to 39. See 

also id. at appendices B, C, and D. 

As specified in 40 CFR 50.17(b), the 

1-hour primary SO2 NAAQS is met at an 

ambient air quality monitoring site 

when the 3-year average of the annual 

99th percentile of daily maximum 1- 

hour concentrations is less than or equal 

to 75 ppb. In a year with 365 days of 

valid monitoring data, the 99th 

percentile would be the fourth highest 

daily maximum 1-hour value. The 2010 

SO2 NAAQS, including this form of 

determining compliance with the 

standard, was upheld by the U.S. Court 

of Appeals for the District of Columbia 

Circuit in Nat’l Envt’l Dev. Ass’n’s Clean 

Air Project v. EPA, 686 F.3d 803 (D.C. 

Cir. 2012). Because the standard has this 

form, a single exceedance does not 

create a violation of the standard. 

Instead, at issue is whether a source 

operating in compliance with a properly 

set longer term average could cause 

exceedances, and if so the resulting 

frequency and magnitude of such 

exceedances, and in particular whether 

EPA can have reasonable confidence 

that a properly set longer term average 

limit will provide that the average 

fourth highest daily maximum value 

will be at or below 75 ppb. A synopsis 

of how EPA judges whether such plans 

‘‘provide for attainment,’’ based on 

modeling of projected allowable 

emissions and in light of the NAAQS’ 

form for determining attainment at 

monitoring sites follows. 

For SO2 plans based on 1-hour 

emission limits, the standard approach 

is to conduct modeling using fixed 

emission rates. The maximum emission 

rate that would be modeled to result in 

attainment (i.e., in an ‘‘average year’’ 3

which shows three days with maximum 

hourly levels exceeding 75 ppb) is 

labeled the ‘‘critical emission value.’’ 

The modeling process for identifying 

this critical emissions value inherently 

considers the numerous variables that 

affect ambient concentrations of SO2, 

such as meteorological data, background 

concentrations, and topography. In the 

standard approach, the state would then 

provide for attainment by setting a 

continuously applicable 1-hour 

emission limit at this critical emission 

value. 

EPA recognizes that some sources 

have highly variable emissions, for 

example due to variations in fuel sulfur 

content and operating rate, that can 

make it extremely difficult, even with a 

well-designed control strategy, to ensure 

in practice that emissions for any given 

hour do not exceed the critical emission 

value. EPA also acknowledges the 

concern that longer term emission limits 

can allow short periods with emissions 

above the ‘‘critical emissions value,’’ 

which, if coincident with 

meteorological conditions conducive to 

high SO2 concentrations, could in turn 

create the possibility of a NAAQS 

exceedance occurring on a day when an 

exceedance would not have occurred if 

emissions were continuously controlled 

at the level corresponding to the critical 

emission value. However, for several 

reasons, EPA believes that the approach 

recommended in its guidance document 

suitably addresses this concern. First, 

from a practical perspective, EPA 

expects the actual emission profile of a 

source subject to an appropriately set 

longer term average limit to be similar 

to the emission profile of a source 

subject to an analogous 1-hour average 

limit. EPA expects this similarity 

because it has recommended that the 

longer term average limit be set at a 

level that is comparably stringent to the 

otherwise applicable 1-hour limit 

(reflecting a downward adjustment from 

the critical emissions value) and that 

takes the source’s emissions profile into 

account. As a result, EPA expects either 

form of emission limit to yield 

comparable air quality. 

Second, from a more theoretical 

perspective, EPA has compared the 

likely air quality with a source having 

maximum allowable emissions under an 

appropriately set longer term limit, as 

compared to the likely air quality with 

the source having maximum allowable 

emissions under the comparable 1-hour 

limit. In this comparison, in the 1-hour 

average limit scenario, the source is 

presumed at all times to emit at the 

critical emission level, and in the longer 

term average limit scenario, the source 

is presumed occasionally to emit more 

than the critical emission value but on 

average, and presumably at most times, 

to emit well below the critical emission 

value. In an ‘‘average year,’’ compliance 

with the 1-hour limit is expected to 

result in three exceedance days (i.e., 

three days with hourly values above 75 

ppb) and a fourth day with a maximum 

hourly value at 75 ppb. By comparison, 

with the source complying with a longer 

term limit, it is possible that additional 

exceedances would occur that would 

not occur in the 1-hour limit scenario (if 

emissions exceed the critical emission 

value at times when meteorology is 

conducive to poor air quality). However, 

this comparison must also factor in the 

likelihood that exceedances that would 

be expected in the 1-hour limit scenario 

would not occur in the longer term limit 

scenario. This result arises because the 

longer term limit requires lower 

emissions most of the time (because the 

limit is set well below the critical 

emission value), so a source complying 

with an appropriately set longer term 

limit is likely to have lower emissions 

at critical times than would be the case 

if the source were emitting as allowed 

with a 1-hour limit. 

As a hypothetical example to 

illustrate these points, suppose a source 

always emits 1,000 pounds of SO2 per 

hour (lbs/hr), which results in air 

quality at the level of the NAAQS (i.e., 

results in a design value of 75 ppb). 

Suppose further that in an ‘‘average 

year,’’ these emissions cause the 5 

highest maximum daily average 1-hour 

concentrations to be 100 ppb, 90 ppb, 80 

ppb, 75 ppb, and 70 ppb. Then suppose 

that the source becomes subject to a 30- 

day average emission limit of 700 lbs/ 

hr. It is theoretically possible for a 

source meeting this limit to have 

emissions that occasionally exceed 

1,000 lbs/hr, but with a typical 

emissions profile emissions would 

much more commonly be between 600 

and 800 lbs/hr. In this simplified 

example, assume a zero background 

concentration, which allows one to 

assume a linear relationship between 

emissions and air quality. (A nonzero 


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4See also further analyses described in 

rulemaking on the SO2 nonattainment plan for 

Southwest Indiana. In response to comments 

expressing concern that the emission profiles 

analyzed for appendix B represented actual rather 

than allowable emissions, EPA conducted 

additional work formulating sample allowable 

emission profiles and analyzing the resulting air 

quality impact. This analysis provided further 

support for the conclusion that an appropriately set 

longer term average emission limit in appropriate 

circumstances can suitably provide for attainment. 

The rulemaking describing these further analyses 

was published on August 17, 2020, at 85 FR 49967, 

available at https://www.govinfo.gov/content/pkg/ 

FR-2020-08-17/pdf/2020-16044.pdf. A more 

detailed description of these analyses is available in 

the docket for that action, specifically at https://

www.regulations.gov/document?D=EPA-R05-OAR2015-0700-0023. 

5For example, if the critical emission value is 

1,000 lbs/hr of SO2, and a suitable adjustment factor 

is determined to be 70 percent, the recommended 

longer term average limit would be 700 lbs/hr. 

background concentration would make 

the mathematics more difficult but 

would give similar results.) Air quality 

will depend on what emissions happen 

on what critical hours, but suppose that 

emissions at the relevant times on these 

5 days are 800 lbs/hr, 1,100 lbs/hr, 500 

lbs/hr, 900 lbs/hr, and 1,200 lbs/hr, 

respectively. (This is a conservative 

example because the average of these 

emissions, 900 lbs/hr, is well over the 

30-day average emission limit.) These 

emissions would result in daily 

maximum 1-hour concentrations of 80 

ppb, 99 ppb, 40 ppb, 67.5 ppb, and 84 

ppb. In this example, the fifth day 

would have an exceedance that would 

not otherwise have occurred (84 ppb 

under the 30-day average limit 

compared to 70 ppb under the 1-hour 

limit). However, the third day would 

not have an exceedance that otherwise 

would have occurred (40 ppb under the 

30-day average limit compared to 80 

ppb under the 1-hour limit). The fourth 

day would have been below, rather than 

at, 75 ppb (67.5 ppb under the 30-day 

average limit compared to 75 ppb under 

the 1-hour limit). In this example, the 

fourth highest maximum daily 

concentration under the 30-day average 

would be 67.5 ppb. 

This simplified example illustrates 

the findings of a more complicated 

statistical analysis that EPA conducted 

using a range of scenarios using actual 

plant data. As described in appendix B 

of EPA’s April 2014 SO2 nonattainment 

planning guidance, EPA found that the 

requirement for lower average emissions 

is likely to yield as good air quality as 

is required with a comparably stringent 

1-hour limit. Based on analyses 

described in appendix B of its 2014 

guidance and similar subsequent work, 

EPA expects that emission profiles with 

maximum allowable emissions under an 

appropriately set comparably stringent 

30-day average limit are likely to have 

the net effect of no more exceedances 

and as good air quality of an emission 

profile with maximum allowable 

emissions under a 1-hour emission limit 

at the critical emission value.4 This 

result provides a compelling policy 

rationale for allowing the use of a longer 

averaging period, in appropriate 

circumstances where the facts indicate 

this result can be expected to occur. 

The question then becomes whether 

this approach, which is likely to 

produce a lower number of overall 

exceedances even though it may 

produce some unexpected exceedances 

above the critical emission value, meets 

the requirement in section 110(a)(1) and 

172(c)(1) for state implementation plans 

to ‘‘provide for attainment’’ of the 

NAAQS. For SO2, as for other 

pollutants, it is generally impossible to 

design a nonattainment plan in the 

present that will guarantee that 

attainment will occur in the future. A 

variety of factors can cause a welldesigned attainment plan to fail and 

unexpectedly not result in attainment, 

for example if meteorology occurs that 

is more conducive to poor air quality 

than was anticipated in the plan. 

Therefore, in determining whether a 

plan meets the requirement to provide 

for attainment, EPA’s task is commonly 

to judge not whether the plan provides 

absolute certainty that attainment will 

in fact occur, but rather whether the 

plan provides an adequate level of 

confidence of prospective NAAQS 

attainment. From this perspective, in 

evaluating use of a 30-day average limit, 

EPA must weigh the likely net effect on 

air quality. Such an evaluation must 

consider the risk that occasions with 

meteorology conducive to high 

concentrations will have elevated 

emissions leading to exceedances that 

would not otherwise have occurred, and 

must also weigh the likelihood that the 

requirement for lower emissions on 

average will result in days not having 

exceedances that would have been 

expected with emissions at the critical 

emissions value. Additional policy 

considerations, such as accommodating 

real world emissions variability without 

significant risk of violations, are also 

appropriate factors for EPA to weigh in 

judging whether a plan provides a 

reasonable degree of confidence that the 

plan will lead to attainment. Based on 

these considerations, EPA believes that 

a continuously enforceable limit 

averaged over as long as 30 days, if 

determined in accordance with EPA’s 

guidance, can reasonably be considered 

to provide for attainment of the 2010 

SO2 NAAQS. 

The April 2014 guidance offers 

specific recommendations for 

determining an appropriate longer term 

average limit. The recommended 

method starts with determination of the 

1-hour emission limit that would 

provide for attainment (i.e., the critical 

emission value), then applies an 

adjustment factor to determine the 

(lower) level of the longer term average 

emission limit that would be estimated 

to have a stringency comparable to the 

1-hour emission limit. This method uses 

a database of continuous emission data 

reflecting the type of control that the 

source will be using to comply with the 

SIP emission limits, which (if 

compliance requires new controls) may 

require use of an emission database 

from another source. The recommended 

method involves using these data to 

compute a complete set of emission 

averages, computed according to the 

averaging time and averaging 

procedures of the prospective emission 

limitation. In this recommended 

method, the ratio of the 99th percentile 

among these long term averages to the 

99th percentile of the 1-hour values 

represents an adjustment factor that may 

be multiplied by the candidate 1-hour 

emission limit to determine a longer 

term average emission limit that may be 

considered comparably stringent.5 The 

guidance also addresses a variety of 

related topics, such as the potential 

utility of setting supplemental emission 

limits, such as mass-based limits, to 

reduce the likelihood and/or magnitude 

of elevated emission levels that might 

occur under the longer term emission 

rate limit. 

Preferred air quality models for use in 

regulatory applications are described in 

appendix A of EPA’s Guideline on Air 

Quality Models (40 CFR part 51, 

appendix W). In 2005, EPA promulgated 

AERMOD as the Agency’s preferred 

near-field dispersion modeling for a 

wide range of regulatory applications 

addressing stationary sources (for 

example in estimating SO2

concentrations) in all types of terrain 

based on extensive developmental and 

performance evaluation. Supplemental 

guidance on modeling for purposes of 

demonstrating attainment of the SO2

standard is provided in appendix A to 

the April 23, 2014 SO2 nonattainment 

area SIP guidance document referenced 

above. Appendix A provides extensive 

guidance on the modeling domain, the 

source inputs, assorted types of 

meteorological data, and background 

concentrations. Consistency with the 

recommendations in this guidance is 

generally necessary for the attainment 


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6EPA–450/4–80–023R, June 1985. 

demonstration to offer adequately 

reliable assurance that the plan provides 

for attainment. 

As stated previously, attainment 

demonstrations for the 2010 1-hour 

primary SO2 NAAQS must demonstrate 

future attainment and maintenance of 

the NAAQS in the entire area 

designated as nonattainment (i.e., not 

just at the violating monitor). This is 

demonstrated by using air quality 

dispersion modeling (see appendix W to 

40 CFR part 51) that shows that the mix 

of sources, enforceable control 

measures, and emission rates in an 

identified area will not lead to a 

violation of the SO2 NAAQS. For a 

short-term (i.e., 1-hour) standard, EPA 

believes that dispersion modeling, using 

allowable emissions and addressing 

stationary sources in the affected area 

(and in some cases those sources located 

outside the nonattainment area which 

may affect attainment in the area) is 

technically appropriate, efficient and 

effective in demonstrating attainment in 

nonattainment areas because it takes 

into consideration combinations of 

meteorological and emission source 

operating conditions that may 

contribute to peak ground-level 

concentrations of SO2.

The meteorological data used in the 

analysis should generally be processed 

with the most recent version of 

AERMET. Estimated concentrations 

should include ambient background 

concentrations, should follow the form 

of the standard, and should be 

calculated as described in section 

2.6.1.2 of the August 23, 2010 

clarification memo on ‘‘Applicability of 

appendix W Modeling Guidance for the 

1-hr SO2 National Ambient Air Quality 

Standard’’ (U.S. EPA, 2010a). 

IV. Review of Modeled Attainment Plan 

The following discussion evaluates 

various features of the modeling that 

Wisconsin used in its attainment 

demonstration. 

A. Model Selection 

Wisconsin’s attainment 

demonstration used AERMOD, the 

preferred model for this application. 

Wisconsin’s January 2016 submittal 

used version 15181 of this model, which 

was the most recent version at that time. 

However, the supplemental modeling 

that Wisconsin submitted in March 

2021 used version 19191, which is the 

current regulatory version of AERMOD. 

EPA finds this selection appropriate. 

Wisconsin’s receptor grid and 

modeling domain for the Rhinelander 

area followed the recommended 

approaches from EPA’s Guideline on Air 

Quality Models (40 CFR part 51, 

appendix W). Receptor spacing for each 

modeled facility was every 25 meters 

out to a distance of 500 meters from 

each source, then every 50 meters to 

1,000 meters, every 100 meters out to 3 

kilometers, every 250 meters out to 6 

kilometers, and every 500 meters out to 

10 kilometers. 

Wisconsin determined that the 

Rhinelander area should be modeled 

with rural dispersion coefficients, as 

Ahlstrom-Munksjo ̈ is surrounded by 

less than 50% of land classified as 

industrial, commercial, or dense 

residential within 3 kilometers, as 

recommended by EPA’s Guideline on 

Air Quality Models. Therefore, EPA 

concurs with Wisconsin’s determination 

that this area warrants being modeled 

with rural dispersion coefficients. 

B. Simulation of Downwash 

Modeling of emissions from 

Ahlstrom-Munksjo ̈ has historically 

underpredicted concentrations 

measured at a nearby monitor. When 

winds blow from this facility toward the 

monitor, the emissions traverse a corner 

of the building. Under these 

circumstances, the building appears to 

cause enhanced eddies in the air flow, 

known as corner vortices, which in 

certain circumstances appear to result in 

a substantial enhancement of downwash 

of emissions to ground level and 

substantially greater concentrations than 

are modeled using the standard 

downwash algorithm in AERMOD. 

Recognizing these issues, the 

company contracted for a wind tunnel 

study, carried out by Cermak Peterka 

Petersen (CPP), to assess the magnitude 

of this effect and to support a more 

accurate assessment of downwash at 

this facility. This study supported the 

conclusion that the discrepancy 

between modeled and monitored SO2

concentrations were due to the corner 

vortex phenomenon, a phenomenon that 

is described in EPA’s ‘‘Guideline for 

Determination of Good Engineering 

Practice Stack Height (Technical 

Support Document for the Stack Height 

Regulations).’’ 6 The wind tunnel study 

showed that as the wind approaches the 

corner of the Ahlstrom-Munksjo ̈

building, vortices are created that act to 

increase the SO2 concentrations 

downwind of the building. Analysis of 

these results suggested that the 

influence of these corner vortices vary 

by wind speed. Ahlstrom-Munksjo ̈’s 

consultants, AECOM and CPP, 

developed an equation estimating a 

multiplier, varying by wind speed, by 

which to estimate the impact of 

downwash in this case, i.e., a multiplier 

by which to multiply concentrations 

estimated in absence of downwash to 

estimate concentrations reflecting the 

downwash induced by this facility. The 

wind tunnel study focused on 

concentrations in the direction with the 

most enhanced downwash but applied 

the same adjustment in all directions. 

Since there is less downwash in 

directions less influenced by corner 

vortices, EPA considers this approach 

conservative in maximizing estimated 

downwash effects on concentrations. 

Wisconsin’s 2016 SIP submittal relied 

on modeling Ahlstrom-Munksjo ̈ using a 

stack height of 90 meters. For this 

facility, the ‘‘formula good engineering 

practice (GEP) stack height’’ computed 

according to the formula in EPA’s stack 

height regulations (defined at 40 CFR 

51.100(ii)(2)(ii)) is 75 meters. EPA 

disapproved the 2016 submittal because 

EPA’s stack height regulations prohibit 

credit for a stack above formula GEP 

stack height unless the state meets 

requirements specified in those 

regulations for the level of control at the 

facility. Wisconsin’s 2021 submittal 

meets EPA’s stack height regulations by 

applying a limit demonstrated to 

provide attainment with a stack at the 

creditable height of 75 meters. 

The wind tunnel studies primarily 

simulated a stack with a height of 85 

meters, with another run simulating a 

stack with a height of 90 meters. These 

runs indicated the following equation to 

estimate the ratio of concentrations 

expected with the building as compared 

concentrations without the building: 


lotter on DSK11XQN23PROD with PROPOSALS1EP22JY21.023</GPH>

Equation 1: ( 

( 1 __ 1 )2) R = A exp _ Uairpor~z Umax + l 
38648 Federal Register / Vol. 86, No. 138 / Thursday, July 22, 2021 / Proposed Rules 

The variable R is the ratio multiplier 

that is applied to the hourly emission 

rate file used in AERMOD. The Uairport 

and Umax values represent the actual 

hourly wind speed measured at the 

Rhinelander airport and the maximum 

wind speed, i.e., wind speed exceeded 

less than 1% of the time, of 10.8 meters 

per second. The A and B parameters are 

best-fit coefficients. The A parameter, 

plus 1, represents the maximum 

multiplier that can be applied to the 

hourly emissions. 

While this equation was originally 

derived to assess the wind-speeddependent influence of downwash with 

a 90-meter stack, the influence of 

downwash for a 75-meter stack may be 

derived based on these same 85-meter 

and 90-meter results by using a best-fit 

coefficient (A) that is specific to a 75- 

meter stack. The best-fit coefficient was 

originally developed using wind tunnel 

data at an 85-meter stack height. This 

coefficient was then adjusted using 

observed and predicted concentration 

ratios, from the wind tunnel 

information, to determine the 

appropriate coefficient for a 75-meter 

stack height. For a 75-meter stack, 

Wisconsin applied the above equation 

with a value of A of 0.826 and B of 

0.174. 

Wisconsin did not modify any 

algorithms or computer code in 

AERMOD to reflect this enhancement of 

the influence of downwash. Instead, 

Wisconsin implemented this 

enhancement by using modified model 

inputs. Wisconsin first examined hourly 

wind speeds. Wisconsin computed 

hourly downwash multipliers based on 

the above equation. Ordinarily, 

Wisconsin would run AERMOD using a 

fixed emission rate reflecting the 

allowable emission rate, but in this case 

Wisconsin input an hourly varying 

emission rate in which each hour’s 

input value equaled the fixed emission 

rate (reflecting the allowable emission 

rate) times that hour’s downwash 

multiplier. For example, for an hour 

with a wind speed of 5 meters per 

second, for which the above equation 

gives a downwash multiplier of 1.564, 

the modeled emission rate for that hour 

reflected multiplication times 1.564. 

This multiplier gives the expected ratio 

of concentrations with the magnitude of 

downwash at this facility as compared 

to the concentrations expected if no 

downwash were occurring. Therefore, 

Wisconsin estimated hourly 

concentrations with Ahlstrom-Munksjo ̈- 

specific downwash by modeling the 

facility without downwash but 

incorporating the expected impact of 

downwash at this facility by increasing 

the emission rate modeled for each hour 

accordingly. 

EPA views Wisconsin’s modeling as 

applying an alternate model under the 

terms of 40 CFR 51 appendix W section 

3.2.2.b.2. Under the alternative model 

criteria discussed in section 3.2.2.b.2, it 

must be shown that the alternative 

model performs better for a given 

application than the recommended 

model, using a statistical analysis. The 

State of Wisconsin evaluated the 

performance of the alternative model 

from both a theoretical and a 

performance perspective. This 

information was included in the public 

notice which preceded Wisconsin 

finalizing its submittal. The Wisconsin 

analysis showed that the alternative 

model predicted a design value slightly 

above the monitored design value using 

the recent three years of monitoring 

data, 2017–2019. The most recent three 

years reflect the impact of emissions 

exiting the 90-meter stack. Recent 

meteorological data, processed for 

modeling purposes, was not available. 

Consequently, the comparison was 

conducted using the full five years of 

meteorology applied for the attainment 

demonstration. 

Additional comparisons were 

conducted that examined, on a year-toyear basis, how well the alternative 

model was performing compared to the 

regulatory version of the model and 

compared to monitoring data. That 

analysis only used emissions from 

boiler B26, which vents through Stack 

S09, when the boiler was actually 

operating, essentially non-summer 

months for the years 2017–2019. This 

supplemental modeling was conducted 

using a grid focused on a 400-meter by 

400-meter area around the monitor to 

the north of Ahlstrom-Munskjo ̈. Again, 

5 years of meteorological data (2011– 

2015) was used in the modeling. 

The model to monitor comparison 

used High 1st High concentrations, the 

average of the top 26 values, fractional 

bias, and 99th percentile values. The 

results of the comparison showed that 

the alternative model performed 

consistently better than the regulatory 

version, that is it predicted higher 

concentrations than the standard 

version of AERMOD. Additionally, the 

year-by-year comparisons to the 

monitored data showed that the 

alternative model produced 

underestimates for one year, 

overestimates for one year, and very 

similar estimates for the third year. 

There was considerable year-to-year 

variability, as one would expect. 

Consequently, the alternative model was 

viewed to be acceptable based on the 

theoretical aspects of its development, 

the superior performance compared to 

the recommended model, and the 

overall unbiased nature of the 

alternative model’s predictions. 

Wisconsin’s alternate model 

characterization was reviewed and 

concurred with on May 28, 2021 by 

EPA’s Model Clearinghouse under 

EPA’s Guideline on Air Quality Models 

criteria for alternate models. EPA 

Region 5’s request for concurrence and 

EPA’s Model Clearinghouse 

concurrence letters are included in the 

docket for this action. 

C. Meteorological Data 

Wisconsin used Rhinelander-Oneida 

County Airport (KRHI) surface data and 

Green Bay, Wisconsin upper air data, 

years 2011–1015, for modeling the 

Rhinelander area. The surface station is 

located less than 5 kilometers from 

Ahlstrom-Munksjo ̈ and is located in 

similar rolling terrain. Given the close 

proximity of the surface station and the 

similarity in surrounding terrain, EPA 

finds the use of the KRHI airport data, 

combined with the Green Bay upper air 

data to be appropriate, representative 

meteorological data sets for assessing 

dispersion at the facility. 

D. Emissions Data 

Wisconsin included all point sources 

within 50 kilometers of Rhinelander in 

its modeling analysis. These sources 

included boilers B26 (sometimes coal 

fired) and B28 (natural gas and oil fired) 

at Ahlstrom-Munksjo ̈, the Kerry Inc. 

facility (formerly Red Arrow Foods), 

and the PCA facility. Wisconsin found 

that no other sources were close enough 

to cause significant concentration 

gradients. Boilers B20, B21, B22, and 

B23 at Ahlstrom-Munksjo ̈ were shut 

down in 2014, and their 

decommissioning is included in a 

federally enforceable permit, so they 

were not included in the modeling 

analysis. Wisconsin determined that 

boiler B26, which vents through stack 

S09, was primarily responsible for the 

Rhinelander area nonattainment 

designation, as the modeling results 

show that boiler B26 accounts for 94–95 

percent of the total SO2 concentration in 

the area depending on the boiler load. 

Therefore, boiler B26 was modeled at 

both minimum and maximum loads. 

The Kerry Inc. and PCA sources, as well 

as Ahlstrom-Munksjo ̈ boiler B28, were 

modeled at their current permitted 

maximum allowable SO2 emissions, as 

contained in federally enforceable 

permits. 

E. Emission Limits 

An important prerequisite for 

approval of an attainment plan is that 


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7For more discussion on stack height, see EPA’s 

November 25, 2020 proposed partial approval and 

partial disapproval (85 FR 75273). 

8To be precise, the emission rates that Wisconsin 

modeled reflected 2.56 lbs/MMBTU times the 

allowable operating rate of 260 MMBTU/hour times 

the hour-specific downwash multiplier discussed 

above. 

9 ‘‘Method 19—Determination of Sulfur Dioxide 

Removal Efficiency and Particulate Matter, Sulfur 

Dioxide, and Nitrogen Oxide Emission Rates’’ (40 

CFR part 60, appendix A). 

the emission limits that provide for 

attainment be quantifiable, fully 

enforceable, replicable, and 

accountable. See General Preamble at 

13567–68. The limit for AhlstromMunksjo ̈ is expressed as a 24-hour 

average limit. Therefore, part of the 

review of Wisconsin’s attainment plan 

must address the use of this limit, both 

with respect to the general suitability of 

using such limits for this purpose and 

with respect to whether the particular 

limits included in the plan have been 

suitably demonstrated to provide for 

attainment. The first subsection that 

follows addresses the enforceability of 

the limits in the plan, and the second 

subsection that follows addresses in 

particular the 24-hour average limit. 

1. Enforceability 

In preparing its plan, Wisconsin 

adopted a revision to a previously 

approved construction permit, Air 

Pollution Control Construction Permit 

Revision 15–DMM–128–R1, governing 

the Ahlstrom-Munksjo ̈ SO2 emissions. 

These permit revisions were adopted by 

Wisconsin following established, 

appropriate public review procedures. 

The revised permit limits boiler B26 

emission rates to 2.38 pounds per 

million British Thermal Unit (lbs/ 

MMBTU) on a 24-hour average basis. 

This limit is more stringent than the 

previously approved limit of 3.0 lbs/ 

MMBTU on a 24-hour average basis. 

The 3.0 lbs/MMBTU limit was included 

as part of Wisconsin’s 2016 attainment 

demonstration that EPA disapproved in 

its March 23, 2021 rulemaking. In 

accordance with EPA policy, the 24- 

hour average limit is set at a lower level 

than the emission rate used in the 

attainment demonstration; the 

relationship between these two values is 

discussed in more detail in the 

following section. Additionally, the 

revised permit limits the maximum heat 

input to boiler B26 to 260 MMBTU/hour 

and requires that stack SO9 be a 

minimum of 75 meters (246 feet) above 

ground, as opposed to the previous 

boiler B26 limit of 300 MMBTU/hour 

and requirement that stack S09 be a 

minimum of 90 meters (296 feet) off the 

ground.7 The permit compliance date 

for Ahlstrom-Munksjo ̈ is December 31, 

2021. EPA finds that this construction 

permit revision provides for permanent 

enforceability. 

2. Longer Term Average Limits 

Ahlstrom-Munksjo ̈ requested a limit 

expressed as a 24-hour average limit in 

order to have a more robust limit, i.e., 

a limit based on more values that would 

be less prone to indicate noncompliance 

based on ordinary fluctuations in 

emissions. In accordance with EPA’s 

April 2014 guidance for SO2

nonattainment plans, Wisconsin 

therefore adjusted its limit, reducing the 

limit for purposes of assuring 

comparable stringency to the 1-hour 

limit that it otherwise would have 

adopted. 

Although compliance with this limit 

will be determined on the basis of 

continuous emissions monitoring 

system (CEMS) data, the facility does 

not have a sufficient historical record of 

CEMS data to be able to evaluate sourcespecific emissions variability for 

purposes of determining a sourcespecific factor by which to adjust the 1- 

hour limit for this source. Instead, 

Wisconsin determined its 24-hour 

average limit by applying one of the 

national average adjustment factors 

listed in appendix D of EPA’s guidance. 

In particular, Wisconsin set its 24-hour 

average limit at 93 percent of the 

modeled emission rate, reflecting the 

national average adjustment factor that 

EPA found among facilities without 

emission control equipment. While the 

facility operates dry sorbent injection 

equipment to control hydrogen chloride 

(HCl) emissions so as to meet the 

maximum available control technology 

requirements for industrial boilers, HCl 

is generally much easier to control than 

SO2, and the information about the 

facility’s sorbent usage provided in 

Wisconsin’s submittal supports a 

conclusion that sorbent injection likely 

reduces SO2 emissions by less than one 

percent. Therefore, sorbent usage may 

be presumed to have very little impact 

on the variability of SO2 emissions at 

this facility, and the national average 

adjustment factor for facilities without 

control equipment is likely to provide 

the best estimate of the appropriate 

degree of adjustment to determine a 24- 

hour limit that is comparably stringent 

to the 1-hour limit that otherwise would 

have been established. 

Wisconsin set its limit at 2.38 lbs/ 

MMBTU, corresponding to 93 percent of 

the 2.56 lbs/MMBTU emission rate that 

Wisconsin modeled.8 Although 

appendix D of EPA’s guidance reports 

average adjustment factors based on 

99th percentile values among lbs/hr 

data rather than among lbs/MMBTU 

data, EPA generally finds that lbs/hr 

data show greater variability than lbs/ 

MMBTU data, and so use of an 

adjustment factor determined from 

analysis of lbs/hr data is likely to yield 

a conservative (more stringent) result. 

The Ahlstrom-Munksjo ̈ 24-hour 

average SO2 emissions will be 

calculated by summing the emissions 

rates of each 1-hour operating period 

and dividing by the number of operating 

hours for that calendar day. Although 

EPA recommends that the average 

values be calculated by summing the 

total emissions and dividing by the total 

heat input for each day, this approach 

is infeasible for Ahlstrom-Munksjo ̈. 

Because Ahlstrom-Munksjo ̈ is using 

Method 19, calculating lbs/MMBTU SO2

concentration without evaluating either 

the mass or the heat input,9 the facility 

does not obtain the hourly mass or heat 

input values to support a calculation of 

daily total mass or daily total heat input. 

As the differences in results of the two 

approaches are expected to be minimal, 

EPA concurs with Wisconsin’s 

approach. 

Ahlstrom-Munksjo ̈ requested that 

Wisconsin specify compliance 

determination procedures for days with 

fewer hours of data (generally, days 

with fewer hours of operation) in order 

to ensure robust compliance 

determinations, specifically to ensure 

that compliance is determined on the 

basis of a minimum of 18 hours of data. 

For days with fewer than 24 but at least 

18 hours of data, compliance will be 

determined by averaging the emissions 

rates from the hours of operation. For 

operating days with fewer than 18 hours 

of data, compliance will be determined 

by averaging all the values from that day 

along with all the values from the most 

recent day with at least 18 hours of 

valid data. EPA supports the principle 

of ensuring that compliance with a longterm average limit should be based on 

a robust data set. Wisconsin’s approach 

also is consistent with the principle that 

the facility shall be accountable for 

emissions at all times, i.e., that days 

with fewer hours of data shall not be 

disregarded but rather shall be included 

in a suitably constructed compliance 

determination. Therefore, EPA 

concludes that Wisconsin is using an 

appropriate approach for addressing 

days with fewer hours of data. 

Based on a review of the State’s 

submittal, EPA believes that the 24- 

hour-average limit for Boiler B26 at 

Ahlstrom-Munksjo ̈ provides a suitable 

alternative to establishing a 1-hour 

average emission limit for this source. 


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10Wisconsin Department of Natural Resources 

(WDNR) maintains an enforcement program to 

ensure compliance with SIP requirements. The 

Bureau of Air Management houses an active 

statewide compliance and enforcement team that 

works in all geographic regions of the State. WDNR 

refers actions as necessary to the Wisconsin 

Department of Justice with the involvement of 

WDNR. Wis. Stats. 285.83 and Wis. Stats. 285.87 

provide WDNR with the authority to enforce 

violations and assess penalties, to ensure that 

required measures are ultimately implemented. 

EPA finds that Wisconsin used an 

appropriate adjustment factor, yielding 

an emission limit that has comparable 

stringency to the 1-hour average limit 

that the State determined would 

otherwise have been necessary to 

provide for attainment. While the 24- 

average limit allows occasions in which 

emissions may be higher than the level 

that would be allowed with the 1-hour 

limit, the State’s limit compensates by 

requiring average emissions to be lower 

than the level that would otherwise 

have been required by a 1-hour average 

limit. For the reasons described above 

and explained in more detail in EPA’s 

April 2014 guidance for SO2

nonattainment plans, EPA finds that 

appropriately set longer term average 

limits provide a reasonable basis by 

which nonattainment plans may 

provide for attainment. Based on its 

review of this general information as 

well as the particular information in 

Wisconsin’s plan, EPA finds that the 24- 

hour-average limit for boiler B26 at 

Ahlstrom-Munksjo ̈ is a suitable 

alternative to establishing a 1-hour limit 

on emissions from this boiler. 

F. Background Concentrations 

Wisconsin determined background 

concentrations for the Rhinelander area 

using 2013–2015 data from the Horicon 

(Dodge County) monitor, which is 

approximately 250 kilometers south of 

Rhinelander. The background 

concentration values that Wisconsin 

used varied by month and hour of the 

day and ranged from 1.40 micrograms 

per cubic meter (mg/m3) to 14.1 mg/m3

with an average value of 4.87 mg/m3. 

EPA agrees that the values from the 

Horicon monitor are representative for 

background concentration estimates. 

G. Summary of Results 

Modeling for the Rhinelander Area in 

Wisconsin’s March 2021 submittal 

showed a design value of 74.8 ppb 

(195.8 mg/m3). This resulted from 

modeling the Ahlstrom-Munksjo ̈ boiler 

B26 at maximum load, combined with 

all other area sources and including a 

background concentration. The run was 

conducted with emissions at 2.56 lbs/ 

MMBTU, a level that corresponds in 

stringency to the 2.38 lbs/MMBTU 24- 

hour average emission limit that 

Wisconsin adopted and submitted and 

is more stringent than the previous 24- 

hour emission limit of 3.0 lbs/MMBTU. 

Therefore, EPA concludes that 

Wisconsin’s plan provides for 

attainment in this area. 

V. Review of Other Plan Requirements 

A. RACM/RACT 

CAA section 172(c)(1) states that 

nonattainment plans shall provide for 

the implementation of all RACM as 

expeditiously as practicable (including 

such reductions in emissions from 

existing sources in the area as may be 

obtained through the adoption, at a 

minimum, of RACT) and shall provide 

for attainment of the national primary 

ambient air quality standards. CAA 

section 172(c)(6) requires plans to 

include enforceable emissions 

limitations, and such other control 

measures as may be necessary or 

appropriate to provide for attainment of 

the NAAQS. In its March 23, 2021 

rulemaking, EPA disapproved 

Wisconsin’s 2016 attainment plan 

because the Ahlstrom-Munksjo ̈

emissions limits (3.0 lbs/MMBTU 24- 

hour average SO2 limit and 300 

MMBTU/hr operating limit) provided in 

the plan were not calculated in 

compliance with the stack height 

regulations. Therefore, the plan could 

not be considered to provide an 

appropriate attainment demonstration, 

and it did not demonstrate RACM/ 

RACT or meet the requirement for 

necessary emissions limitations or 

control measures. Wisconsin’s revised 

plan for attaining the 1-hour SO2

NAAQS in the Rhinelander area is 

based on a variety of measures, 

including more stringent SO2 emissions 

and operating limits (2.38 lbs/MMBTU 

24-hour average SO2 limit and 260 

MMBTU/hr operating limit) for 

Ahlstrom-Munksjo ̈, which were 

calculated in compliance with the stack 

height regulations. Wisconsin’s plan 

requires compliance with these 

measures by December 31, 2021. 

Wisconsin has determined that these 

measures suffice to provide for 

attainment. EPA concurs and proposes 

to conclude that the State has satisfied 

the requirement in section 172(c)(1) and 

(6) to adopt and submit all RACM/RACT 

and emissions limitations or control 

measures as needed to attain the 

standards as expeditiously as 

practicable. 

B. Reasonable Further Progress (RFP) 

In its March 23, 2021 rulemaking, 

EPA concluded that Wisconsin had not 

satisfied the requirement in section 

172(c)(2) to provide for RFP toward 

attainment. Wisconsin’s 2016 

attainment plan did not demonstrate 

that the implementation of the control 

measures required under the plan were 

sufficient to provide for attainment of 

the NAAQS in the Rhinelander SO2

nonattainment area consistent with EPA 

requirements (in particular consistent 

with EPA stack height regulations). 

Therefore, a compliance schedule to 

implement those controls was not 

sufficient to provide for RFP. 

Wisconsin’s revised plan requires 

compliance by December 31, 2021. 

Wisconsin concludes that this is an 

ambitious compliance schedule, as 

described in April 2014 guidance for 

SO2 nonattainment plans, and 

concludes that this plan therefore 

provides for RFP in accordance with the 

approach to RFP described in EPA’s 

2014 guidance. EPA concurs and 

proposes to conclude that the plan 

provides for RFP. 

C. Contingency Measures 

As noted above, EPA guidance 

describes special features of SO2

planning that influence the suitability of 

alternative means of addressing the 

requirement in section 172(c)(9) for 

contingency measures for SO2, such that 

in particular an appropriate means of 

satisfying this requirement is for the 

State to have a comprehensive 

enforcement program that identifies 

sources of violations of the SO2 NAAQS 

and to undertake an aggressive followup for compliance and enforcement. 

Wisconsin’s plan provides for satisfying 

the contingency measure requirement in 

this manner.10 EPA concurs and 

proposes to approve Wisconsin’s plan 

for meeting the contingency measure 

requirement in this manner. 

VI. What action is EPA taking? 

EPA is proposing to approve 

Wisconsin’s SIP submission, which the 

State submitted to EPA on March 29, 

2021 to supplement the prior SIP it had 

submitted on January 22, 2016 and 

supplemented on July 18, 2016, and 

November 29, 2016, for attaining the 

2010 1-hour SO2 NAAQS for the 

Rhinelander area and for meeting other 

nonattainment area planning 

requirements. This SO2 attainment plan 

includes Wisconsin’s attainment 

demonstration for the Rhinelander area. 

The plan also addresses requirements 

for RFP, RACT/RACM, and contingency 

measures. EPA has previously 

concluded that Wisconsin has 

addressed the requirements for 


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11Orders AM–94–38 and AM–15–01 were issued 

to the facility’s prior owner, Expera, but the orders 

continued to limit the facility’s emissions after it 

was acquired by Ahlstrom-Munksjo ̈. 

emissions inventories for the 

Rhinelander area and nonattainment 

area NSR. EPA has determined that 

Wisconsin’s Rhinelander SO2 plan 

meets applicable requirements of 

section 172 of the CAA. 

Wisconsin’s Rhinelander SO2 plan is 

based on the emissions limits specified 

in Air Pollution Control Construction 

Permit Revision 15–DMM–128–R1. 

Wisconsin seeks EPA to approve several 

elements of the permit, including the 

permit cover sheet, emissions 

limitations for Ahlstrom-Munksjo ̈

(Conditions A.3.a.(1)–(3)), compliance 

demonstration (Conditions A.3.b.(1)– 

(3)), reference test methods, 

recordkeeping and monitoring 

requirements (Conditions A.3.c.(1)–(5) 

and A.3.c.(7)–(9)), and the effective date 

(Condition YYY.1.a.(1)). Wisconsin did 

not seek approval of limits and test 

methods associated with oil sulfur 

content. Wisconsin stated that limits on 

the portion of emissions from oil are 

unnecessary to comply with the 24-hour 

SO2 emission limit and the boiler heat 

input limit, and attainment is ensured 

by limits on total emissions from boiler 

B26. EPA concurs with Wisconsin’s 

rationale, and therefore EPA is 

proposing to approve these elements of 

the permit. 

Additionally, EPA is proposing to 

replace the previously approved consent 

and administrative orders (AM–94–38 

and AM–15–01) governing the 

Ahlstrom-Munksjo ̈ emission limits 11

with the elements of Wisconsin’s Air 

Pollution Control Construction Permit 

Revision 15–DMM–128–R1 specified 

above. This replacement would not be 

effective until December 31, 2021, 

which is the revised permit compliance 

date for Ahlstrom-Munksjo ̈. Section 

110(l) of the CAA states that EPA ‘‘shall 

not approve a revision of a plan if the 

revision would interfere with any 

applicable requirement . . .’’ Since 

Permit 15–DMM–128–R1 contains a 

more stringent SO2 limit for AhlstromMunksjo ̈ (2.38 lbs/MMBTU on a 24-hour 

average basis) than the previous orders 

(3.0 lbs/MMBTU on a 24-hour average 

basis), and since Wisconsin has 

demonstrated that the limit in Permit 

15–DMM–128–R1 provides for 

attainment without need for the limits 

in the prior orders, EPA concludes that 

Section 110(l) does not prohibit EPA 

from replacing the prior orders with the 

newer permit, and EPA is proposing to 

act in accordance with this Wisconsin 

request. 

EPA is taking public comments for 

thirty days following the publication of 

this proposed action in the Federal 

Register. EPA will take all comments 

into consideration in the final action. If 

this approval is finalized, it would 

terminate the sanctions clock started 

under CAA section 179 resulting from 

EPA’s partial disapproval of the prior 

SIP, as well as EPA’s duty to promulgate 

a FIP for the area under CAA section 

110(c) that resulted from the previous 

partial disapproval. 

VII. Incorporation by Reference 

In this rule, EPA is proposing to 

include in a final EPA rule regulatory 

text that includes incorporation by 

reference. In accordance with 

requirements of 1 CFR 51.5, EPA is 

proposing to incorporate by reference 

the specific portions of Wisconsin Air 

Pollution Control Construction Permit 

Revision 15–DMM–128–R1, effective 

December 31, 2021, as described in 

section VI. above. EPA has made, and 

will continue to make, these documents 

generally available through 

www.regulations.gov and at the EPA 

Region 5 Office (please contact the 

person identified in the FOR FURTHER

INFORMATION CONTACT section of this 

preamble for more information). 

Also in this document, as described in 

section VI, EPA is proposing to remove 

provisions of the EPA-Approved 

Wisconsin Source Specific 

Requirements from the Wisconsin State 

Implementation Plan, which is 

incorporated by reference in accordance 

with the requirements of 1 CFR part 51. 

VIII. Statutory and Executive Order 

Reviews 

Under the CAA, the Administrator is 

required to approve a SIP submission 

that complies with the provisions of the 

CAA and applicable Federal regulations. 

42 U.S.C. 7410(k); 40 CFR 52.02(a). 

Thus, in reviewing SIP submissions, 

EPA’s role is to approve state choices, 

provided that they meet the criteria of 

the CAA. Accordingly, this action 

merely approves state law as meeting 

Federal requirements and does not 

impose additional requirements beyond 

those imposed by state law. For that 

reason, this action: 

• Is not a significant regulatory action 

subject to review by the Office of 

Management and Budget under 

Executive Orders 12866 (58 FR 51735, 

October 4, 1993) and 13563 (76 FR 3821, 

January 21, 2011); 

• Does not impose an information 

collection burden under the provisions 

of the Paperwork Reduction Act (44 

U.S.C. 3501 et seq.); 

• Is certified as not having a 

significant economic impact on a 

substantial number of small entities 

under the Regulatory Flexibility Act (5 

U.S.C. 601 et seq.); 

• Does not contain any unfunded 

mandate or significantly or uniquely 

affect small governments, as described 

in the Unfunded Mandates Reform Act 

of 1995 (Pub. L. 104–4); 

• Does not have federalism 

implications as specified in Executive 

Order 13132 (64 FR 43255, August 10, 

1999); 

• Is not an economically significant 

regulatory action based on health or 

safety risks subject to Executive Order 

13045 (62 FR 19885, April 23, 1997); 

• Is not a significant regulatory action 

subject to Executive Order 13211 (66 FR 

28355, May 22, 2001); 

• Is not subject to requirements of 

Section 12(d) of the National 

Technology Transfer and Advancement 

Act of 1995 (15 U.S.C. 272 note) because 

application of those requirements would 

be inconsistent with the CAA; and 

• Does not provide EPA with the 

discretionary authority to address, as 

appropriate, disproportionate human 

health or environmental effects, using 

practicable and legally permissible 

methods, under Executive Order 12898 

(59 FR 7629, February 16, 1994). 

In addition, the SIP is not approved 

to apply on any Indian reservation land 

or in any other area where EPA or an 

Indian tribe has demonstrated that a 

tribe has jurisdiction. In those areas of 

Indian country, the rule does not have 

tribal implications and will not impose 

substantial direct costs on tribal 

governments or preempt tribal law as 

specified by Executive Order 13175 (65 

FR 67249, November 9, 2000). 

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Intergovernmental relations, 

Reporting and recordkeeping 

requirements, Sulfur oxides. 

Dated: July 13, 2021. 

Cheryl Newton, 

Acting Regional Administrator, Region 5. 

[FR Doc. 2021–15464 Filed 7–21–21; 8:45 am] 

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